[require] GLSL >= 1.10 [vertex shader] void main() { gl_Position = gl_Vertex; } [fragment shader] uniform vec4 color; void main() { const vec4 red = vec4(1.0, 0.0, 0.0, 0.0); const vec4 green = vec4(0.0, 1.0, 0.0, 0.0); if (false && color.b != 0.0) gl_FragColor = red; else gl_FragColor = green; } [test] draw rect -1 -1 2 2 probe rgb 1 1 0.0 1.0 0.0